A known fuel cell vehicle runs on electric power that is generated in a fuel cell. The fuel cell is supplied with fuel, such as hydrogen gas, to generate the electric power. Such fuel cell vehicle normally has a high pressure tank that contains the fuel under high pressure to be used for the fuel cell. A valve system is mounted to a mouthpiece of the high pressure tank. The valve system has a gas flow passage and various valves that are located on the gas flow passage. The gas flow passage and the various valves are integrated together into the valve system.
Japanese Patent Application Publication No. 2006-242225 (JP-A-2006-242225) discloses a valve system for a gas container. The valve system has a first passage and a second passage that communicate the gas container with the outside. The first passage is designed to flow gas into the gas container. The second passage is designed to flow the gas out of the gas container. The valve system further has a communication passage and a shut-off valve. The communication passage connects the first passage to the second passage. The shut-off valve is located on the communication passage. The shut-off valve is normally closed. However, the shut-off valve is opened in an emergency where a valve on the second passage, which is located closer to the gas container than a connecting point of the second passage with the communication passage, is malfunctioned and cannot open. This allows gas in the gas container to flow through the first passage, the communication passage, and the second passage in order, thereby to depressurize the gas in the gas container.
The valve system that is disclosed in JP-A-2006-242225 also has a relief passage and a fusible plug valve. The relief passage is designed to relieve gas from the gas container to the outside. The fusible plug valve is located on the relief passage. According to this construction, when the fusible plug valve opens at a high temperature, the relief passage is communicated with the outside, thereby to depressurize the gas in the gas container.
Japanese Patent Application Publication No. 2008-232408 (JP-A-2008-232408) discloses a safety valve for a high pressure gas container. The safety valve has a function of discharging gas through the valve that is opened by moving a valve element when a fusible plug in the valve fuses at a high temperature. The safety valve also has a function of discharging gas through the valve that is opened by manually moving the valve element. The safety valve has a main body and a valve housing. The main body contains the valve element and the fusible plug. The valve housing contains the main body that is screw-joined to the valve housing. In the safety valve that has the aforementioned construction, the main body is rotated manually using a tool. This causes the main body together with the valve element and the fusible plug that are contained in the main body to all move toward the outside of the valve housing, so that the valve is opened to discharge gas.
As disclosed in JP-A-2006-242225, the valve system of a high pressure tank for a vehicle according to the related art has a fusible plug valve. The fusible plug valve is located on a release passage (the relief passage) that is designed to release gas from the high pressure tank to the outside. The fusible plug valve releases the gas in the high pressure tank to the outside at a high temperature. As disclosed in 2006-242225, the valve system of the high pressure tank for a vehicle further has a manual pressure reducing valve. The manual pressure reducing valve is located on the communication passage that communicates an inlet passage (the first passage) with an outlet passage (the second passage). The inlet passage flows gas into the high pressure tank. The outlet passage flows the gas out of the high pressure tank. When a valve that is located on the outlet passage, for example a main stop valve, is malfunctioned, the manual pressure reducing valve is opened manually to flow gas but of the high pressure tank in order to depressurize the gas in the high pressure tank. As described above, the valve system of the high pressure tank for a vehicle according to the related art is provided with two types of valves that operate in an emergency: the fusible plug valve and the manual pressure reducing valve. Moreover, this valve system has separate passages for these two types of valves to be placed. Therefore, a main body of the valve system tends to be larger in size. However, the vehicle has only a limited space for the high pressure tank installed on the vehicle, and thus should have only a tight space for the valve system to the high pressure tank.
JP-A-2008-232408 discloses the safety valve in which the fusible plug valve and the manual valve are combined together. It is conceivable that the safety valve that is disclosed in JP-A-2008-232408 is used in the valve system of the high pressure tank for a vehicle in order to reduce the size of the valve system. However, solely using this safety valve in the valve system produces the following problems. To be more specific, the safety valve that is disclosed in JP-A-2008-232408 is designed to exert gas pressure on the fusible plug through the valve element whenever the valve is closed. If the safety valve thus-designed is used in the valve system of the high pressure tank for a vehicle, the valve element, on which high gas pressure (for example 70 MPa) from the high pressure tank is exerted, causes the fusible plug to deform, so that valve is opened. This can cause the gas to be released from the high pressure tank to the outside even at a normal temperature.